JP2005053755A - Epitaxial thin film of oxide and its manufacturing method - Google Patents
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- 239000010409 thin film Substances 0.000 title claims abstract description 53
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 17
- 239000010408 film Substances 0.000 claims abstract description 112
- 239000000758 substrate Substances 0.000 claims abstract description 55
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 39
- 239000001301 oxygen Substances 0.000 claims abstract description 38
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 38
- 238000000137 annealing Methods 0.000 claims abstract description 33
- 238000000034 method Methods 0.000 claims abstract description 25
- 238000000151 deposition Methods 0.000 claims abstract description 17
- 230000008021 deposition Effects 0.000 claims abstract description 8
- 230000001678 irradiating effect Effects 0.000 claims abstract description 8
- 238000010438 heat treatment Methods 0.000 claims description 21
- 238000005137 deposition process Methods 0.000 claims 1
- 238000004549 pulsed laser deposition Methods 0.000 claims 1
- 230000015572 biosynthetic process Effects 0.000 description 33
- 239000002356 single layer Substances 0.000 description 27
- 238000002441 X-ray diffraction Methods 0.000 description 14
- 239000013078 crystal Substances 0.000 description 11
- 238000001228 spectrum Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 239000004020 conductor Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 230000000704 physical effect Effects 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000001069 Raman spectroscopy Methods 0.000 description 2
- 239000010410 layer Substances 0.000 description 2
- 239000000696 magnetic material Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910002367 SrTiO Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000000407 epitaxy Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- -1 ferroelectrics Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000000608 laser ablation Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
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Abstract
Description
本発明は、パルスレーザー蒸着法による酸化物エピタキシャル薄膜の作製方法、およびこの作製方法により得られる酸化物エピタキシャル薄膜に関する。 The present invention relates to a method for manufacturing an oxide epitaxial thin film by a pulse laser deposition method, and an oxide epitaxial thin film obtained by this manufacturing method.
パルスレーザー蒸着法（以下、ＰＬＤ（Pulse Laser Deposition）法という。）は、エネルギー密度の高いパルスレーザー光をターゲット（薄膜の材料となる物質）表面に照射することにより、ターゲット表面の材料を瞬間的に剥離し、放出されるプラズマ化された原子、分子をターゲットと対向して配置された基板上に堆積させて薄膜を作製する方法である。この方法は、レーザー光を吸収する物質であれば高融点のものでも容易に薄膜化が可能であること、ターゲットの元素組成をほぼ反映した薄膜を形成可能であること、膜厚の原子層レベルでの制御が可能であること等から、幅広い範囲の材料の薄膜化に利用されている。また、高い真空度を必要とせず、様々なガス雰囲気下での成膜が可能であることから、特に、酸化物薄膜の成膜法として有効に利用されており、数多くの報告例がある。例えば、数百度の高温で高いプロトン伝導性を示し、プロトン導電性固体電解質としてセンサーデバイスや燃料電池への利用が考えられている、ある種のペロブスカイト型酸化物についての薄膜作製の報告例がある（例えば、非特許文献１及び非特許文献２参照）。
The pulse laser deposition method (hereinafter referred to as PLD (Pulse Laser Deposition) method) irradiates the target surface material instantaneously by irradiating the surface of the target (substance that becomes a thin film material) with pulsed laser light with high energy density. A thin film is prepared by depositing plasma atoms and molecules that are peeled off and released onto a substrate disposed opposite to a target. This method can easily form a thin film even if it has a high melting point as long as it absorbs laser light, can form a thin film that almost reflects the elemental composition of the target, and has an atomic layer level of film thickness. It is used for thinning a wide range of materials. In addition, since a film can be formed under various gas atmospheres without requiring a high degree of vacuum, it is particularly effectively used as a method for forming an oxide thin film, and there are many reports. For example, there is a report on the preparation of thin films for certain perovskite-type oxides that exhibit high proton conductivity at high temperatures of several hundred degrees and are considered to be used for sensor devices and fuel cells as proton conductive solid electrolytes. (For example, refer
従来、ＰＬＤ法による酸化物薄膜の成膜は、一般に、基板の温度を７００℃程度の高温に保って、行われている。これは、成膜時の基板の温度が室温程度の低温では、一般に得られる酸化物膜が非晶質となってしまうためであり、また、非晶質の酸化物膜を酸素中または空気中にて加熱（アニール）することで結晶化することは可能であるが、非常に高い温度が必要であり、７００℃程度の温度のアニールでは、多結晶質または配向性の低い結晶質の膜しか得ることができないためである。
一方、高温での成膜では酸化物結晶から酸素が欠損しやすいので、それを防ぐために一般には〜１Ｐａ程度の酸素雰囲気で成膜は行われる。
Conventionally, the formation of an oxide thin film by the PLD method is generally performed while maintaining the temperature of the substrate at a high temperature of about 700 ° C. This is because, when the temperature of the substrate during film formation is low, such as room temperature, an oxide film that is generally obtained becomes amorphous. In addition, an amorphous oxide film is not formed in oxygen or air. It is possible to crystallize by heating (annealing), but a very high temperature is required. In annealing at a temperature of about 700 ° C., only a polycrystalline or low-orientation crystalline film can be obtained. It is because it cannot be obtained.
On the other hand, since oxygen tends to be deficient from the oxide crystal in the film formation at a high temperature, the film formation is generally performed in an oxygen atmosphere of about 1 Pa to prevent it.
薄膜作製において、ラジカル酸素やラジカル窒素など反応性の高いガスを利用した方法も知られている。しかし、酸化物膜の成膜においては、基板温度を高温にして成膜する場合のラジカル酸素利用の有効性は見出されていない。 A method using a highly reactive gas such as radical oxygen or radical nitrogen is also known for thin film production. However, in the formation of an oxide film, the effectiveness of utilizing radical oxygen when the film is formed at a high substrate temperature has not been found.
ところで、酸化物薄膜は、デバイスへの利用を念頭に、その物性を改善する方法が種々試みられている。その一つとして、２種類以上の異なる材料からなるエピタキシャル薄膜を原子層レベルで繰り返し積層させた超格子が挙げられる。超格子では、積層界面に生じる格子不整合（格子定数のミスマッチ）による応力を利用して酸化物薄膜に格子歪（格子定数の変化）を導入し、酸化物薄膜の物性を変化させることができる。このような超格子の応用例は、磁性体、強誘電体など様々な酸化物材料であり、先に述べたプロトン導電性のペロブスカイト型酸化物でも超格子は作製され、超格子にすることでプロトン導電性が変化することが報告されている（例えば、非特許文献１参照）。
単層膜においても、基板によっては基板と膜との界面で格子不整合が生じる。数百ナノメートル程度の膜厚の単層膜では、応力緩和が起きるので、基板との格子不整合による格子歪が現れる報告例は知られていない。
Even in a single layer film, lattice mismatch occurs at the interface between the substrate and the film depending on the substrate. In a single-layer film having a thickness of about several hundred nanometers, stress relaxation occurs, so there is no known report example in which lattice strain due to lattice mismatch with the substrate appears.
上記の通り、従来、ＰＬＤ法により酸化物のエピタキシャル薄膜、すなわち配向性が良く結晶質な酸化物薄膜を得るためには、基板の温度を高温に保ち、酸素雰囲気中で成膜を行う必要があり、そのため、成膜装置には、成膜中に基板を高温に保持し、しかもおよそ〜１Ｐａ程度の酸素雰囲気中で高温に耐え得る特別な加熱機構を必要とし、装置が複雑になってしまっていた。 As described above, conventionally, in order to obtain an oxide epitaxial thin film by the PLD method, that is, a crystalline oxide thin film with good orientation, it is necessary to keep the temperature of the substrate high and perform film formation in an oxygen atmosphere. Therefore, the film forming apparatus requires a special heating mechanism that can hold the substrate at a high temperature during film formation and can withstand the high temperature in an oxygen atmosphere of about ˜1 Pa, and the apparatus becomes complicated. It was.
このような状況に鑑み、本発明は、ＰＬＤ法による酸化物エピタキシャル薄膜の作製において、成膜条件を容易なものとし、成膜装置の構造を簡素化することのできる、酸化物エピタキシャル薄膜の作製方法を提供することを課題とする。
また、本発明は、格子歪を含んだ単層の酸化物エピタキシャル薄膜を提供することも課題とする。
In view of such circumstances, the present invention provides an oxide epitaxial thin film that can facilitate the film forming conditions and simplify the structure of the film forming apparatus in the preparation of an oxide epitaxial thin film by the PLD method. It is an object to provide a method.
Another object of the present invention is to provide a single-layer oxide epitaxial thin film containing lattice strain.
上記課題を解決するために、本発明は、１０〜１００℃に保持した基板上に、ラジカル酸素を照射しながら、パルスレーザー蒸着法により酸化物膜を蒸着する成膜工程と、酸化物膜を蒸着温度より高温で加熱するポストアニール工程とを有することを特徴とする酸化物エピタキシャル薄膜の作製方法を提供する。 In order to solve the above-described problems, the present invention provides a film forming process for depositing an oxide film by pulse laser deposition while irradiating radical oxygen on a substrate maintained at 10 to 100 ° C., and an oxide film. And a post-annealing step of heating at a temperature higher than the deposition temperature.
このように、ＰＬＤ法による酸化物薄膜の作製において、成膜時にラジカル酸素を照射し、さらに成膜後に高温でアニールすることにより、成膜時の基板温度が１００℃以下の低温であっても、エピタキシャルな薄膜が作製できるので、基板の加熱機構に高い耐久性が要求されず、加熱機構及び成膜装置を簡素化することができる。
成膜時の基板温度は、好ましくは１０〜５０℃であり、より好ましくは１５〜２５℃である。特に、基板加熱を必要としない室温付近とするのが、成膜装置に加熱機構を設ける必要がなく装置を極めて簡素化でき、また基板温度の上昇・降下する工程がなくなり薄膜作製プロセスも簡略化できるので、望ましい。
In this way, in the production of an oxide thin film by the PLD method, radical oxygen is irradiated at the time of film formation, and annealing is performed at a high temperature after the film formation, so that the substrate temperature at the time of film formation is as low as 100 ° C. or less. Since an epitaxial thin film can be produced, high durability is not required for the heating mechanism of the substrate, and the heating mechanism and the film forming apparatus can be simplified.
The substrate temperature at the time of film formation is preferably 10 to 50 ° C, more preferably 15 to 25 ° C. In particular, near room temperature, which does not require substrate heating, makes it possible to greatly simplify the apparatus without the need to provide a heating mechanism for the film deposition apparatus, and to simplify the thin film fabrication process by eliminating the process of raising and lowering the substrate temperature. It is desirable because it can.
成膜工程におけるラジカル酸素の照射は、５×１０14〜５×１０15atomos/cm2/sの照射量で行うことができる。また、ラジカル酸素は、ビーム状で基板の成膜面に向けて行う。
ラジカル酸素は、原子状酸素（atomic oxygen）とも呼ばれ、酸素分子よりも反応性が高い。本発明においてラジカル酸素は、ＰＬＤ法による成膜工程においてレーザーによりプラズマ化された原子、分子の酸化反応を促進させ、さらに結合した酸素が、酸素雰囲気中で成膜された膜の場合と異なり、ポストアニールにより膜の配向性を上げ得る状態になるように作用していると推定している。
Radical oxygen irradiation in the film formation step can be performed at an irradiation dose of 5 × 10 14 to 5 × 10 15 atomos / cm 2 / s. In addition, radical oxygen is beam-shaped toward the film formation surface of the substrate.
Radical oxygen, also called atomic oxygen, is more reactive than oxygen molecules. In the present invention, radical oxygen promotes the oxidation reaction of atoms and molecules converted into plasma by a laser in a film formation step by the PLD method, and further, the bonded oxygen is different from the case of a film formed in an oxygen atmosphere. It is presumed that post-annealing acts so that the film can be oriented.
成膜後のポストアニール工程は、酸素雰囲気、空気雰囲気などで行うことができる。あるいは、真空中でラジカル酸素を照射しながら行うこともできる。配向性が良く結晶質な膜を得る上ではラジカル酸素を照射しながら行うことが好ましいが、装置及びポストアニール工程の簡素化の点で、１気圧酸素雰囲気または１気圧空気中で行う方がより好ましく、１気圧酸素雰囲気で行うのが特に好ましい。 The post-annealing step after film formation can be performed in an oxygen atmosphere, an air atmosphere, or the like. Or it can also carry out, irradiating radical oxygen in a vacuum. In order to obtain a crystalline film with good orientation, it is preferable to carry out irradiation with radical oxygen, but in terms of simplifying the apparatus and the post-annealing process, it is more preferable to carry out in a 1 atmosphere oxygen atmosphere or 1 atmosphere air. It is preferable to carry out in a 1 atmosphere oxygen atmosphere.
ポストアニール工程における酸化物膜の加熱温度と加熱時間は、膜の配向性が十分に上がり、設備的にも作業効率的にも負担のない範囲で設定する。加熱温度としては６００〜７５０℃が好ましく、加熱時間としては１〜１０時間が好ましい。 The heating temperature and heating time of the oxide film in the post-annealing step are set within a range where the film orientation is sufficiently improved and there is no burden in terms of equipment and work efficiency. The heating temperature is preferably 600 to 750 ° C., and the heating time is preferably 1 to 10 hours.
本発明の酸化物エピタキシャル薄膜の作製方法は、酸化物のなかでもペロブスカイト型酸化物の薄膜作製に特に有効である。
また、本発明の作製方法により、基板との間に格子不整合が生じていても、基板の格子に揃った酸化物薄膜を得ることができる。すなわち、バルクより格子定数が小さい、または大きい状態で薄膜化された、格子歪を含んだ酸化物単層膜を得ることができる。
The method for producing an oxide epitaxial thin film of the present invention is particularly effective for producing a perovskite oxide thin film among oxides.
Further, according to the manufacturing method of the present invention, an oxide thin film aligned with the lattice of the substrate can be obtained even when lattice mismatch occurs between the substrate and the substrate. That is, it is possible to obtain an oxide single-layer film including lattice strain that is thinned with a lattice constant smaller or larger than that of the bulk.
本発明によれば、ＰＬＤ法による酸化物薄膜の成膜を１００℃以下の低温で行ってもエピタキシャルな薄膜が作製可能となるので、成膜装置において従来必要とされていた高温・酸素雰囲気下の使用に耐え得る基板加熱機構を必要とせず、ＰＬＤシステムを簡素化することができる。
特に、室温付近での成膜が可能なので、この場合、成膜装置には基板加熱機構そのものを必要としないので、基板加熱機構からの不純物による薄膜汚染がなくなる。また基板温度の上昇・降下が不要になるので、薄膜作製プロセスも簡略化することができる上に、バッチ処理によってエピタキシャル薄膜の作製に必要な時間も短縮できる。
According to the present invention, an epitaxial thin film can be formed even when an oxide thin film is formed at a low temperature of 100 ° C. or lower by the PLD method. Therefore, the PLD system can be simplified without requiring a substrate heating mechanism that can withstand the use of the PLD system.
In particular, since film formation can be performed near room temperature, the film formation apparatus does not require the substrate heating mechanism itself, and thus thin film contamination due to impurities from the substrate heating mechanism is eliminated. Further, since the substrate temperature does not need to be raised or lowered, the thin film production process can be simplified, and the time required for producing the epitaxial thin film can be shortened by batch processing.
また、本発明によれば、格子歪を含んだ単層膜の作製が容易になる。単層の酸化物薄膜においても、格子歪を導入することによりその物性を各種デバイスに適するように改善することが可能となる。例えば、強誘電体や磁性体でペロブスカイト型構造を持つ酸化物が
あるが、本発明により単層膜であっても格子歪を導入するにとによりその誘電率や磁気的性質を調整することが可能となる。
Further, according to the present invention, it becomes easy to produce a single layer film including lattice strain. Even in the case of a single-layer oxide thin film, the physical properties can be improved so as to be suitable for various devices by introducing lattice strain. For example, there are ferroelectric and magnetic oxides with a perovskite structure, but the present invention can adjust the dielectric constant and magnetic properties by introducing lattice strain even in the case of a single layer film. It becomes possible.
以下、本発明についてさらに詳細に説明する。
前述した通り、本発明の酸化物エピタキシャル薄膜の作製方法は、（１）１００℃以下に保持した基板上に、ラジカル酸素を照射しながら、ＰＬＤ法により酸化物膜を蒸着する成膜工程と、（２）酸化物膜を蒸着温度より高温で加熱するポストアニール工程とを有する。
Hereinafter, the present invention will be described in more detail.
As described above, the method for producing an oxide epitaxial thin film of the present invention includes (1) a film forming step of depositing an oxide film by a PLD method while irradiating radical oxygen on a substrate held at 100 ° C. or lower; (2) a post-annealing step of heating the oxide film at a temperature higher than the deposition temperature.
上記（１）の成膜工程では、真空容器中で、作製する薄膜と同一組成の酸化物の焼結体等のターゲットに高エネルギー密度のレーザー光をパルス状に照射し、ターゲット表面から原子、分子をプラズマ化して瞬間的に剥離して対向する基板上に蒸着させて、酸化物膜の成膜を行う。
ターゲットには作製する酸化物薄膜と同一組成の焼結体や圧粉体などを用いることができる。特に、焼結体は真空容器を汚しにくい点で好ましい。相対密度９９％以上、純度９９．９９％程度の各種酸化物の焼結体が市販されているので、作製したい酸化物薄膜に応じてそれらを用いることができる。
In the film forming step (1) above, a high energy density laser beam is irradiated in a vacuum container onto a target such as an oxide sintered body having the same composition as the thin film to be produced, and atoms, Molecules are converted into plasma, are instantaneously peeled off, and vapor-deposited on the opposite substrate to form an oxide film.
As the target, a sintered body or a green compact having the same composition as the oxide thin film to be produced can be used. In particular, the sintered body is preferable in that it does not easily contaminate the vacuum vessel. Since sintered bodies of various oxides having a relative density of 99% or more and a purity of about 99.99% are commercially available, they can be used according to the oxide thin film to be produced.
酸化物膜を蒸着させる基板は、単結晶基板を用いる。単結晶基板は、薄膜を作製しようとする酸化物の結晶と、格子不整合が小さく、対称性が合うものを選択することが好ましい。単結晶基板は、成膜工程に先立ち、高温における熱処理、酸によるエッチング処理などにより表面処理をしておくことが好ましい。 A single crystal substrate is used as the substrate on which the oxide film is deposited. As the single crystal substrate, it is preferable to select a single crystal substrate having a small lattice mismatch and symmetry with the oxide crystal for which a thin film is to be formed. Prior to the film formation step, the single crystal substrate is preferably subjected to surface treatment by heat treatment at high temperature, etching treatment with acid, or the like.
これらターゲット及び基板は、真空容器中では、互いに対向するように配置する。ターゲットと基板との間の距離は、通常、数ｃｍから１０ｃｍ程度である。
ターゲット及び基板を配置後、一端、真空容器を真空度が少なくとも１０-5Ｐａ程度まで真空引きすることが、ターゲットや基板の表面に付着しているＨ2Ｏ等のガスを排気することができるので、好ましい。
成膜時には、ラジカル酸素を照射しながら酸化物膜の蒸着を行うので、真空容器中の真空度はおよそ１０-2Ｐａ程度まで低下する。
These target and substrate are arranged so as to face each other in the vacuum vessel. The distance between the target and the substrate is usually about several cm to 10 cm.
After placing the target and the substrate, the vacuum vessel is evacuated to a vacuum degree of at least about 10 −5 Pa, so that gas such as H 2 O adhering to the surface of the target or substrate can be exhausted. Therefore, it is preferable.
At the time of film formation, the oxide film is deposited while irradiating radical oxygen, so that the degree of vacuum in the vacuum vessel is reduced to about 10 −2 Pa.
成膜の際には、ターゲットは自転させることが、レーザー光の照射によるターゲット表面の形状変化の影響を抑えるためには、好ましい。
また、基板も回転させることが好ましい。これは、レーザー光の照射によってターゲット表面から剥離される原子、分子のプラズマの基板上に達する径には限りがあり、その範囲内で物質が基板上に蒸着するため、より広い面積に均一に成膜するためである。
In film formation, it is preferable to rotate the target in order to suppress the influence of the shape change of the target surface due to laser light irradiation.
It is also preferable to rotate the substrate. This is because the diameter of atoms and molecules that are peeled off from the target surface by laser irradiation reaches the substrate, and the substance is deposited on the substrate within that range. This is for forming a film.
成膜に用いるレーザー光は、通常、紫外領域の波長のものを選ぶ。紫外レーザーとしては、ＸｅＣｌ、ＫｒＦ、ＡｒＦ等のエキシマーレーザーが挙げられる。また、Ｎｄ：ＹＡＧレーザーの４倍波などを用いることもできる。
レーザー光は、エネルギー密度を高めるためにターゲット表面に焦点を絞って照射する。焦点の面積とレーザー光のエネルギー値とから決まる、ターゲットに入射するレーザー光のパワー密度により、ターゲット表面から剥離する原子、分子の状態や成膜速度が変化するので、良好な膜質を得るため適当に調整する。
The laser beam used for film formation is usually selected with a wavelength in the ultraviolet region. Examples of the ultraviolet laser include excimer lasers such as XeCl, KrF, and ArF. In addition, a quadruple wave of an Nd: YAG laser can be used.
The laser beam is irradiated focused on the target surface in order to increase the energy density. Appropriate for obtaining good film quality because the state of the atoms and molecules peeled off from the target surface and the film formation speed vary depending on the power density of the laser light incident on the target, which is determined by the focal area and the energy value of the laser light. Adjust to.
上記（２）のポストアニール工程は、上記（１）の成膜工程で得られた酸化物膜に対して行う。
ポストアニール工程は、成膜装置（成膜を行った真空容器）内で成膜後引き続いて行うこともできるが、成膜装置の簡略化を図る意味で、成膜装置から専用のアニール処理装置に移して行うことが好ましい。ここで言うアニール処理装置とは、酸化物膜が蒸着された基板を収納し所望の雰囲気及び温度に保てる容器と、加熱機構とを備え、さらにその他の必要な機能を備えた装置であり、その具体的な仕様は特に制限はない。
The post-annealing step (2) is performed on the oxide film obtained in the film-forming step (1).
The post-annealing step can be performed after film formation in a film formation apparatus (vacuum container in which film formation has been performed), but in order to simplify the film formation apparatus, a dedicated annealing apparatus is used from the film formation apparatus. It is preferable to transfer to The annealing treatment device mentioned here is a device having a container capable of storing a substrate on which an oxide film is deposited and maintaining a desired atmosphere and temperature, a heating mechanism, and further having other necessary functions. The specific specification is not particularly limited.
本発明の方法によりエピタキシャル薄膜を作製できる酸化物の一例として、ＡＢＯ3で表されるペロブスカイト型酸化物が挙げられる。
ペロブスカイト型酸化物としては例えば高温超電導体、強誘電体、磁性体などがあるが、他の例として、数百度の高温でプロトン導電性を示すプロトン導電体がある。ペロブスカイト型酸化物のプロトン導電体としては、ＳｒＺｒＯ3、ＳｒＣｅＯ3、ＳｒＴｉＯ3、ＢａＺｒＯ3、ＢａＣｅＯ3、ＢａＴｉＯ3、ＣａＺｒＯ3等においてＺｒ、Ｃｅ、ＴｉなどＡＢＯ3のＢサイトの４価イオンを一部３価の陽イオン（Ｙ3+、Ｙｂ3+、Ｓｃ3+、Ｅｒ3+など）に置き換えたものが挙げられる。これらのプロトン導電体においても、本発明の方法によりＭｇＯやＳｉなどの単結晶基板上にエピタキシャル薄膜を作製することができる。
An example of an oxide that can produce an epitaxial thin film by the method of the present invention is a perovskite oxide represented by ABO 3 .
Examples of perovskite oxides include high-temperature superconductors, ferroelectrics, and magnetic materials. Other examples include proton conductors that exhibit proton conductivity at a high temperature of several hundred degrees. As a proton conductor of perovskite type oxide, tetravalent ions at the B site of ABO 3 such as Zr, Ce, Ti, etc. in SrZrO 3 , SrCeO 3 , SrTiO 3 , BaZrO 3 , BaCeO 3 , BaTiO 3 , CaZrO 3, etc. Examples thereof include those substituted with trivalent cations (Y 3+ , Yb 3+ , Sc 3+ , Er 3+, etc.). Also in these proton conductors, an epitaxial thin film can be formed on a single crystal substrate such as MgO or Si by the method of the present invention.
＜１＞（株）アルバック製レーザーアブレーション用超高真空容器にＭｇＯ単結晶基板（００１）面（フルウチ化学（株）製）を設置した。室温にて、基板上にラジカル酸素を２×１０15atomos/cm2/sで照射しながら、ラムダフィジックス製ＡｒＦエキシマーレーザーのレーザー光を高純度のＢａＺｒ0.95Ｙ0.05Ｏ3（以下、ＢＺＹという。）ターゲットに入射、ターゲットから３０ｍｍ離して対向させた基板上にＢＺＹの単層膜を蒸着させた。膜厚はおよそ２００ｎｍとした。
同様に、ターゲットをＳｒＺｒ0.95Ｙ0.05Ｏ3（以下、ＳＺＹという。）に換えてＳＺＹの単層膜（膜厚およそ２００ｎｍ）をＭｇＯ基板上に蒸着した。
なお、ターゲットは、９９．９〜９９．９９％の純度のＢａＣＯ3、ＳｒＣＯ3、ＺｒＯ2、Ｙ2Ｏ3を原料として固相反応で作製した。
このようにして、基板上に酸化物膜を蒸着した２つの試料を、次に空気中で７５０℃に保持し１０時間アニールした。
<1> An MgO single crystal substrate (001) surface (manufactured by Furuuchi Chemical Co., Ltd.) was placed in an ultra-high vacuum vessel for laser ablation manufactured by ULVAC. While irradiating the substrate with radical oxygen at 2 × 10 15 atomos / cm 2 / s at room temperature, the laser light of an ArF excimer laser manufactured by Lambda Physics is referred to as high-purity BaZr 0.95 Y 0.05 O 3 (hereinafter referred to as BZY). ) A BZY single layer film was deposited on the substrate that was incident on the target and faced away from the target by 30 mm. The film thickness was about 200 nm.
Similarly, the target was changed to SrZr 0.95 Y 0.05 O 3 (hereinafter referred to as SZY), and a single-layer film (thickness: about 200 nm) of SZY was deposited on the MgO substrate.
The target was prepared by solid phase reaction using BaCO 3 , SrCO 3 , ZrO 2 , and Y 2 O 3 having a purity of 99.9 to 99.99% as raw materials.
In this way, the two samples with the oxide film deposited on the substrate were then annealed for 10 hours at 750 ° C. in air.
また、ラジカル酸素の照射を行わず、室温、１０-1Ｐａの酸素雰囲気下でＭｇＯ基板上に単層膜を蒸着させ、その後、空気中で７５０℃に保持し１０時間アニールした比較用の試料をＢＺＹ、ＳＺＹのそれぞれについて作製した。 In addition, a comparative sample in which a single layer film was deposited on an MgO substrate in an oxygen atmosphere at room temperature and 10 −1 Pa without irradiation with radical oxygen, and then kept in air at 750 ° C. and annealed for 10 hours. Were prepared for each of BZY and SZY.
上記のように作製した試料をＸ線回折装置により、Ｘ線回折パターンを測定した。測定結果を図１及び図２に示す。
Ｘ線回折パターンにより、酸素雰囲気中で成膜した膜はポストアニール後もほとんど配向性のない多結晶質の膜で有るのに対し、ラジカル酸素照射下で成膜した膜はポストアニール後に配向性の高い膜となっていることが分かった。なお、図１及び図２において、as grownとは、成膜後ポストアニール前の状態を指し、この状態では、ラジカル酸素照射下で成膜した膜と酸素雰囲気中で成膜した膜とで、Ｘ線回折パターンに大きな違いは見られなかった。
The X-ray diffraction pattern of the sample prepared as described above was measured using an X-ray diffractometer. The measurement results are shown in FIGS.
According to the X-ray diffraction pattern, the film deposited in an oxygen atmosphere is a polycrystalline film with little orientation after post-annealing, whereas the film deposited under radical oxygen irradiation is oriented after post-annealing. It was found that the film was high. 1 and 2, as grown refers to a state after film formation and before post-annealing. In this state, a film formed under radical oxygen irradiation and a film formed in an oxygen atmosphere There was no significant difference in the X-ray diffraction pattern.
また、ラジカル酸素照射下で成膜して試料については、Ｘ線回折極点図の測定を行い、面内方向（基板と平行な面内）の配向性を調べた。図３にＳＺＹの単層膜の（１１０）面極点図を、図４にＳＺＹ単層膜及びＢＺＹ単層膜それぞれの（１１０）面に対するφスキャンスペクトルを示す。
図３及び図４に示されるように、ＳＺＹ、ＢＺＹの薄膜は、ＭｇＯ基板に揃ってエピタキシャル成長していることが分かった。
In addition, X-ray diffraction pole figures were measured for samples formed under radical oxygen irradiation, and the orientation in the in-plane direction (in the plane parallel to the substrate) was examined. FIG. 3 shows a (110) plane pole figure of the SZY single layer film, and FIG. 4 shows a φ scan spectrum for the (110) plane of each of the SZY single layer film and the BZY single layer film.
As shown in FIGS. 3 and 4, it was found that the SZY and BZY thin films were epitaxially grown along with the MgO substrate.
＜２＞次に、ＢＺＹ、ＳＺＹそれぞれについて、上記＜１＞と同様にしてラジカル酸素照射下で単層膜をＭｇＯ基板上に蒸着させた後、ポストアニールの温度及び時間をそれぞれ６００〜７５０℃、１〜１０時間の範囲で変化させた試料を作製した。作製した試料のＸ線回折パターン及びＸ線回折極点図を測定したところ、配向性の高いエピタキシャルな膜となっていることが確認された。
ＢＺＹの単層膜について、図５及び図６に、ポストアニールの条件によるＸ線回折パターンのピーク強度及び（１１０）面φスキャンスペクトルのピーク幅の違いを示す。この結果より、ポストアニールの条件により膜の結晶性に違いがあることが分かった。加熱温度６５０〜７００℃で５〜１０時間アニールした場合に特に結晶性の良い膜が得られる。なお、このポストアニールの条件による膜の結晶性の違いは、ラマン散乱スペクトルの測定結果からＳＺＹの単層膜でも確認できた（図７参照）。
<2> Next, for each of BZY and SZY, after depositing a single layer film on the MgO substrate under irradiation of radical oxygen in the same manner as in the above <1>, the temperature and time of post-annealing are set to 600 to 750 ° C., respectively. Samples changed in the range of 1 to 10 hours were prepared. When the X-ray diffraction pattern and X-ray diffraction pole figure of the prepared sample were measured, it was confirmed that the film was an epitaxial film with high orientation.
Regarding the single-layer film of BZY, FIG. 5 and FIG. 6 show the difference in peak intensity of the X-ray diffraction pattern and peak width of the (110) plane φ scan spectrum depending on the post-annealing conditions. From this result, it was found that the crystallinity of the film varies depending on the post-annealing conditions. A film with particularly good crystallinity is obtained when annealing is performed at a heating temperature of 650 to 700 ° C. for 5 to 10 hours. The difference in the crystallinity of the film depending on the post-annealing conditions was confirmed even in the SZY single-layer film from the measurement result of the Raman scattering spectrum (see FIG. 7).
また、ＳＺＹの単層膜について、図８に、ポストアニールの条件によるＸ線回折パターンのピーク位置の違いを示す。同様な変化はＢＺＹの単層膜についても確認された。この結果より、ポストアニールの条件により積層方向で膜の格子面間隔が異なることが分かった。これはエピタキシーの差により格子歪が変化していると推定される。 FIG. 8 shows the difference in the peak position of the X-ray diffraction pattern depending on the post-annealing conditions for the SZY single layer film. Similar changes were confirmed for the BZY monolayer film. From this result, it was found that the lattice spacing of the film differs in the stacking direction depending on the post-annealing conditions. This is presumed that the lattice strain changes due to the difference in epitaxy.
＜３＞さらに、ＢＺＹ、ＳＺＹそれぞれについて、基板温度を６５０℃に保持したＭｇＯ基板上に単層膜を蒸着させた以外は、上記＜１＞と同様にして、高温成膜の試料を作製した。
高温成膜の試料、及び上記＜１＞でラジカル酸素の照射下の室温で作製した低温成膜の試料のそれぞれについて、Ｘ線回折パターンの測定結果から（１００）面間隔を求めた。その結果を、参照用のバルク結晶の値を含めて、表１に示す。
<3> Further, for each of BZY and SZY, samples for high-temperature film formation were prepared in the same manner as in the above <1> except that a single layer film was deposited on an MgO substrate maintained at a substrate temperature of 650 ° C. .
The (100) plane spacing was determined from the X-ray diffraction pattern measurement results for each of the high temperature film formation sample and the low temperature film formation sample prepared at room temperature under irradiation of radical oxygen in the above <1>. The results are shown in Table 1, including the value of the reference bulk crystal.
表１に示すように、高温成膜で得られる薄膜の（１００）面間隔はバルク結晶に近い値となる。これはラジカル参照の照射下で成膜しても、酸素雰囲気中で成膜しても同様な結果が得られる。
一方、低温成膜で得られる薄膜の（１００）面間隔は、ＢＺＹ、ＳＺＹいずれの薄膜においてもバルク結晶の値より小さい。ＢＺＹ、ＳＺＹのいずれもＭｇＯ基板と界面で格子不整合が生じるが、本発明の方法により作製した薄膜はポストアニールにより基板に揃うことで、格子が歪み、（１００）面間隔が小さくなると推定される。
As shown in Table 1, the (100) plane spacing of a thin film obtained by high temperature film formation is a value close to that of a bulk crystal. The same result can be obtained whether the film is formed under irradiation of radical reference or in an oxygen atmosphere.
On the other hand, the (100) plane spacing of the thin film obtained by the low temperature film formation is smaller than the value of the bulk crystal in both the BZY and SZY thin films. In both BZY and SZY, lattice mismatch occurs at the interface with the MgO substrate, but it is estimated that the thin film produced by the method of the present invention is aligned with the substrate by post-annealing, thereby distorting the lattice and reducing the (100) plane spacing. The
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| WO2014034794A1 (en) * | 2012-08-29 | 2014-03-06 | トヨタ自動車株式会社 | Solid electrolyte single crystal having perovskite structure and method for producing same |
| CN108110286A (en) * | 2016-11-25 | 2018-06-01 | 中国科学院大连化学物理研究所 | The preparation method of one proton conductive oxide electrolytic thin-membrane |
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| WO2023084274A1 (en) | 2021-11-10 | 2023-05-19 | Silanna UV Technologies Pte Ltd | Epitaxial oxide materials, structures, and devices |
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| JP4644856B2 (en) * | 2005-06-06 | 2011-03-09 | 独立行政法人科学技術振興機構 | Method for producing ferroelectric perovskite-type barium titanate single crystal |
| WO2014034794A1 (en) * | 2012-08-29 | 2014-03-06 | トヨタ自動車株式会社 | Solid electrolyte single crystal having perovskite structure and method for producing same |
| JP5922780B2 (en) * | 2012-08-29 | 2016-05-24 | トヨタ自動車株式会社 | Solid electrolyte single crystal having perovskite structure and method for producing the same |
| CN108110286A (en) * | 2016-11-25 | 2018-06-01 | 中国科学院大连化学物理研究所 | The preparation method of one proton conductive oxide electrolytic thin-membrane |
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